Portable systems, such as mobile electronic devices, which are powered by rechargeable batteries have a problem supporting both USB (Universal Serial Bus) charging state and suspend state functions.
When a rechargeable battery is dead or not present, the mobile electronic device can not operate since it does not have any power. In order for the mobile electronic device to operate, the mobile electronic device is connected to a USB host in order to draw power from the host to both power up the device and recharge the battery. However, when the mobile electronic device is connected to the USB host, USB specifications require that the device initiate enumeration within 100 msec, hereon referred to as “VBUS detection”. Enumeration is the process whereby the device requests permission from the USB host to access the host. In this case, the enumeration request is directed to a request for the mobile electronic device to draw a current/voltage from the USB host in order to power up the mobile electronic device as well as to recharge the dead or non-present battery.
In most cases, it is desired that a battery charger within the mobile electronic device turn on once it receives power from the USB host upon VBUS detection. This causes the battery charger to be enabled so that the current/voltage supplied by the USB host is used for operation of the device and recharging of the battery. This may be referred to as a device charging state. Therefore, when the voltage via the VBUS is applied, the battery charger is enabled and acts as a power source to power up the mobile electronic device and to recharge the battery.
Another common state for the mobile electronic device is a device suspend state. USB specifications require that the total current supplied by the USB host to the mobile electronic device does not exceed 500 μA in the device suspend state. With many mobile electronic devices, 500 μA is not enough current for the processor or CPU in the mobile electronic device to operate and therefore the device is generally powered down. Powering down of the CPU in the mobile electronic device causes all the control signals to default to a low state signal, which causes the battery charger to be enabled. However, since 500 μA is not enough current for operation of the device, it is not desirable for the battery charger to be enabled during the device suspend state. In some other prior art devices, support for the device suspend state is not recognized and the battery charger remains enabled during the device suspend state. In this manner, the 500 μA current limit is not recognized or acknowledged by the mobile electronic device even though it is required by USB specifications.
Furthermore, in some prior art devices, two separate signals to control the device charging state and the device suspend state are used.
It is, therefore, desirable to provide a method and apparatus for handling a charging state and a device suspend state in a mobile electronic device.